The present invention relates to an ink-jet recording sheet, and specifically to an ink-jet recording sheet which results in high quality prints.
Ink-jet recording is carried out by impinging micro-droplets employing various working principles and attaching them onto a recording sheet of paper to record images, letters and the like, and exhibits advantages such as relatively high speed, low noise, easy application for multicolor. At present, it has been increasingly employed in various fields such as printers, facsimile machines, computer terminals and the like.
Requirements for a recording sheet employed in such ink-jet recording system is that the density of printed dots is high, color tone is bright and clear, ink is rapidly absorbed and when printed dots are superimposed, ink should neither run nor blot, the diffusion of a printed dot in the lateral direction should not be greater than needed, and the circumference should be smooth and result in no blurring; and the like.
Specifically, at low rates of ink absorption, when recording is carried out by superimposing at least two color ink droplets, on a recording sheet, droplets result in repellence to cause unevenness, and in the boundary area of different colors, different color inks blot with each other. As a result, image quality tends to be markedly degraded. Therefore, it is required that the recording sheet exhibits high ink absorbability.
In order to solve these problems, conventionally, a great number of techniques have been proposed.
For example, Japanese Patent Publication Open to Public Inspection No. 52-53012 describes a recording sheet in which minimally sized paper is damped with paint employed for surface treatment; Japanese Patent Publication Open to Public Inspection No. 55-5830 describes a recording sheet comprising a support in which an ink-absorbable coating layer is provided on the surface of the support; Japanese Patent Publication Open to Public Inspection No. 56-157 describes a recording sheet comprising a covering layer containing non-colloidal silica powder as a pigment; Japanese Patent Publication Open to Public Inspection No. 57-107873 describes a recording sheet comprising an inorganic pigment and an organic pigment in combination; Japanese Patent Publication Open to Public Inspection No. 58-110287 describes a recording sheet which exhibits a void distribution with two peaks; Japanese Patent Publication Open to Public Inspection No. 62-111782 describes a recording sheet composed of an upper porous layer and a lower porous layer; Japanese Patent Publication Open to Public Inspection Nos. 59-68292, 59-123696, 60-18383, etc. describe a recording sheet having amorphous cracking; Japanese Patent Publication Open to Public Inspection Nos. 61-135786, etc. describe a recording sheet having a fine powder layer; Japanese Patent Publication Open to Public Inspection Nos. 63-252779, 1-108083, 2-136279, 3-65376, 3-27976, etc. describe a recording sheet comprising pigments and fine silica particles having specified physical parameters; Japanese Patent Publication Open to Public Inspection Nos. 57-14091, 60-219083, 60-210984, 61-20797, 61-188183, 5-278324, 6-92011, 6-183134, 7-137431, 7-276789, etc. describe a recording sheet containing fine silica particles such as colloidal silica; Japanese Patent Publication Open to Public Inspection Nos. 2-276671, 3-67684, 3-215082, 3-251488, 4-67986, 4-263983, 5-16517, etc. describe a recording sheet containing fine hydrated alumina particles, and the like.
Of these, because relatively high gloss is obtained, as high quality glossy sheets, void type recording sheets are preferred in which fine voids are formed in the ink receptive layer employing fine inorganic particles and a hydrophilic binder.
When a recording sheet has excessively high gloss, it is found that when a plurality of sheets are fed from a stack, two or more sheets tend to be fed at the same time due to the excessive surface friction, or after ink-jet recording, the gloss of an image area formed by receiving inks tends to decrease.
Hereinafter, a part which has received ink will be denoted an image area, while a part which has not received ink will be denoted a non-image area.
Specifically, regarding the latter, in conventional recording sheets having high gloss, as the gloss of the non-image part, which has not received ink, increases, the print quality tends to be markedly degraded due to a minor decrease in the gloss of the image part. Consequently, in terms of the print quality, only the improvement in the gloss of the non-image part is not sufficient for that as print quality.
In the image quality of conventional ink-jet recording, regarding this point, as major factors, granular appearance and resolution have been areas of concern and even this point has not been of much concern. However, in recent years, due to the emergence of high quality printers, the print image quality has markedly improved and is approaching the level of photographic prints. Thus, the importance of this aspect has increased.
The reason for a decrease in the gloss of an image part decreases is not clarified as yet. However, it is assumed that the decrease is caused by swelling the hydrophilic binder in an ink receptive layer using low-volatile solvents contained in the ink-jet recording ink.
In conventional recording sheets, from such a viewpoint, an approach to improve the print quality has not been carried out. Inventors of the present invention have diligently investigated this point, and as a result, it is revealed that prints with highly excellent image quality are obtained by enhancing the glossiness of the image parts more than the nonimage parts, while specifying the glossiness of the surface to a specific range.
An object of the present invention is to provide an ink-jet recording sheet which has relatively high gloss and results in a high quality print due to a further increase in the gloss when printed by employing an ink-jet method.
Ink-jet recording sheets and embodiments thereof will be described below.
In ink-jet recording sheets comprising a support having thereon a void layer containing fine inorganic particles having a dispersion degree of no more than 2 and a hydrophilic binder as an ink-absorbable layer, having a specular gloss, specified by JIS Z8741, of at least 20 percent at 60 degrees of the surface of said ink absorbable layer, and exhibiting the specular gloss such that 60-degree specular gloss of an ink-recorded part is 3 percent more than that of a nonink-recorded part.
A support is preferably water-resistant.
Fine inorganic particles are preferably silica having an average particle diameter of no more than 100 nm and a hydrophilic binder is preferably polyvinyl alcohol.
A hardener may be incorporated into the void layer.
Examples of hardeners are boric acids or salts thereof.
The support is preferably a water-resistant support having a specular gloss of 20 to 80 percent.